1. Field of the Invention
The present invention relates to a method and an apparatus for manufacturing a metal oxide device, and more particularly to a method and an apparatus for manufacturing a superconducting coated conductor grown epitaxially by using a replication process.
2. Description of the Related Art
Since the discovery of high-temperature superconductors in 1986, a number of studies on superconducting tapes have been actively undertaken. A powder-in-tube (PIT) technique is commercially used to manufacture first-generation superconducting tapes using Bi-2223. This technique is advantageous in terms of its simplified manufacturing process, but has a disadvantage in that since the angle of grain boundaries is increased due to poor in-plane alignment of superconductors, the critical current of the first-generation superconducting tapes does not reach that of single-crystal superconductors.
To solve the problems of the first-generation superconducting tapes, second-generation superconducting tapes using ReBCO, such as YBCO, have attracted attention. The second-generation superconducting tapes are manufactured by forming a thin film on a metal tape, e.g., a Ni alloy tape. Since the second-generation superconducting tapes are highly biaxially aligned, they advantageously have critical current characteristics substantially identical to single crystal superconductors.
Techniques for manufacturing the second-generation superconducting tapes are conducted in such a manner that an oxide high-temperature superconductor, including YBCO, is biaxially aligned in a direction parallel to a thin film. These techniques are largely divided into the following two processes. The first process is one wherein a base, as a substrate for a superconductor thin film, is designed to have a textured structure, and then a superconductor thin film is formed on the base to render it to be biaxially aligned. The second process is one wherein a template layer sandwiched between a base as a substrate and a superconductor thin film is controlled to have a crystallinity close to a single crystal, regardless of the crystallinity of the base.
The first process is referred to as a “rolling assisted biaxially textured substrate (RABiTS) process”, and the second process is referred to as an “ion beam assisted deposition (IBAD) process”. In addition to these processes, various processes, including inclined substrate deposition (ISD) and ion beam texture (ITEX), are currently undergoing trial.
However, superconducting layers of the superconducting tapes manufactured by the conventional processes are biaxially oriented, and exist in a polycrystalline state close to a single crystal. For these reasons, the critical current of the superconducting tapes does not reach a value corresponding to that of single-crystal superconductors due to grain boundaries between crystal particles, causing a problem that advantages inherent to superconductors are not sufficiently attainable.
Further, according to prior arts, particularly, the IBAD process, a non-conductive thin film (e.g., MgO or YSZ) is formed on a support layer supporting a device, and then a superconducting layer is formed thereon. Therefore, the support layer and the superconducting layer are electrically separated from each other, making it impossible to bypass an overcurrent into the support layer. According to the RABiTS process, Ni as a magnetic material is used as the support layer. Accordingly, when a superconducting tape formed on the support layer (Ni) is placed inside a magnetic field, characteristics of the superconducting tape are degraded due to a magnetic field induced by the support layer (Ni).
According to prior arts, since the support layer should have a thickness on the order of several tens to several hundreds of micrometers, there is a limitation in controlling the thickness. In addition, since the deposition of the superconductor thin film is dependant on the kind of constituent materials of the support layer, the choice of the materials is limited.